Headset bearings see a lot of lateral force under braking, and they can shift even with the tightest of tolerances. The bearing rings should, of course, get grease, but the wedge-shaped ring below the top cap is the heart of the headset and often the cause of creaking. Keeping it sloppy will keep your headset tight.
Direct-mount rings see a lot of force as well, and they’re one of the many things that can creak under pedaling load. If you're hunting down some noise in your bottom bracket, this is a place to check.
Thru axles get threaded and unthreaded more often than any other part on our bike. And they're usually aluminum-on-aluminum – not the most durable or scratch-resistant material. As abrasions build up over the months and years, it's more likely to someday seize up. Some grease and care may eventually save you from a really bad day.